The device works very well with my Samsung Galaxy S3 or Nexus 7 (2014). The LED is the charging indicating not clearly visible (light is poor - but is OK). One should know the charging takes the cell phone battery about 8-9 hours only. So twice as long as with the supplied charger to the USB jack.
On my Nexus 7, the USB contacts were broken for loading the battery already after half a year. The Nexus 7 I invite definitely with this device.